Hormone Axis Physiology Flashcards
Which hormones are released from the anterior pituitary?
TSH ACTH FSH + LH GH Prolactin
Which hormones are released from the posterior pituitary?
Oxytocin
ADH
Describe the thyroid axis
Hypothalamus releases thyrotropin-releasing hormone (TRH) –> anterior pituitary releases TSH –> thyroid releases T3 + T4
T3 + T4 exert negative feedback on hypothalamus and pituitary
Describe the adrenal axis
Hypothalamus releases corticotrophin releasing hormone (CRH) –> anterior pituitary releases ACTH –> adrenal glands secrete cortisol
What is the usual pattern of cortisol release?
Pulsatile - peaks first thing in the morning
And in response to stressful stimulus
Describe the growth hormone axis
Hypothalamus releases growth hormone releasing hormone (GHRH) –> anterior pituitary releases GH –> liver releases insulin-like growth factor 1 (IGF-1)
What stimulates the release of parathyroid hormone (PTH)?
Low serum calcium
Low magnesium
High phosphate
What does the release of PTH do?
Increases serum calcium levels by:
- reabsorption of calcium from bone
- increase in calcium absorption in the kidneys
- stimulates kidneys to convert vitamin D3 to calcitriol (active vitamin D)
How does calcitriol help increase serum calcium?
Promotes calcium absorption from food in the small intestine
Where is renin released from and in response to what?
Juxtaglomerular cells in afferent arterioles in the kidney
Released in response to low BP
What does renin do?
Enzyme that converts angiotensinogen (from liver) into angiotensin 1
What happens to angiotensin I?
It is converted to angiotensin II by angiotensin converting enzyme (ACE)
What does angiotensin II do?
Causes vasoconstriction –> increased BP
Also stimulates release of aldosterone from the adrenal glands
What does aldosterone do?
Mineralocorticoid steroid hormone, acts on nephrons to:
- increase sodium reabsorption from distal tubule
- increase potassium secretion from distal tubule
- increase hydrogen secretion from collecting ducts
